Spinning machines usually have a large number of spinning units beside another. EP-A-189 516 discloses a rotor spinning machine having an automatic tender which patrols along the machine and stops at any spinning unit where a yarn break has been detected or spinning has to be restarted. To this end, the automatic tender has a manipulator which after a yarn break, hunts for the yarn end on the package and threads it back as far as the rotor or winds a separate yarn on to a new tube and threads it. A critical factor for satisfactory piecing-up is accurate timing of the various operating sequences after the start of piecing up. To this end, EP-A-0 198 516 suggests using a single control device for the tender to control all the movement sequences after the start of piecing up. This process has proved satisfactory. However, there is a deviation in reaction times between the various machine parts serviced by the tender because of manufacturing tolerances between individual spinning units, with a consequent deviation in the length of overlap between the yarn to be pieced up and the newly formed yarn. Since a single tender patrols many spinning units, considerable time may elapse before the tender discovers a spinning unit with a yarn break if the tender has passed by such unit, for example, shortly before the yarn break.
Piecing-up in air jet spinning machines, as described, for example, in DE-PS 3 413 894 and EP-A 0 107 339, is even more difficult since the spinning speeds of air jet machines are considerably greater than those of rotor spinning machines. For an optimal connection between yarn to be pieced up and new yarn the overlap length should be approximately from 2 to 3 times the average fiber length--e.g. approximately 25-75 mm. At a spinning speed of 240 m/min such an overlap length passes by a position in approximately from 6 to 17 ms. The sequence of movements after the start signal of the tender must therefore be accurate to milliseconds if the connection between the two yarn ends is to be satisfactory.
Accordinq to EP-A-0 107 339, some of the machine parts to be moved in the movement sequence after the start of piecing up, are disposed on the spinning unit and others on the tender. Because the delay in actuation may vary from one spinning unit to another and may have a deviation of several milliseconds at least with respect to conventional changeover valves which may be invalid in a piecing operation, actuation of the moving parts of the spinning machine by the control device of the tender is too inaccurate to ensure an overlap length reproducible with sufficient accuracy.
In U.S. Pat. No. 4,821,504 a travelling automatic tender for doffing at several parallel to each other arranged spinning machines is known. The spinning machines are connected to a common control unit, which is connected by way of a signal line with a control unit for the movement of the automatic tender. This common control unit indicates to the second control unit on the tender, in which direction the tender has to be moved. A lamp on the selected spinning machine is releasing the braking operation and the mechanical coupling with the automatic tender. This device is, however, specifically developed for doffing of spinning machines, and is not for controlling servicing manipulations at a single station of a spinning machine, as required, e.g. for piecing after yarn breakage.
It is an object of the invention, therefore, to provide a process and a textile spinning apparatus for precisely effecting servicing operations such as piecing, cleaning, start-up and others with respect to servicing a plurality of spinning units on a single spinning machine.